And now on to the next problem. After replacing the FPR, car was running reasonably enough to drive. After a couple days, today, during a short drive the car started running like absolute garbage and would barely stay moving, steadily getting worse till it barely limped into the spot at home. It threw a code the instant it started running badly. Code 44. Oxygen sensor circuit. Now this sensor isn't all that old. It was changed within the last 8 years, althought the care was barely driven during that time. Would that code/oxygen sensor cause the car to barely function at all if it was going bad? 91 Trans Am, TPI, stock.

 

On your last datalog I reviewed the o2 sensor was bouncing around as normal. That said it was only idling.

What brand sensor did you get? The Bosch sensors have a pretty bad reputation. The Delco AFS 74 seems to be the better one.

If you got a log on this run, it'd be interesting to see the O2 sensor output.

If the O2 fails at low voltage, the ECM will interpret that as an overly lean condition and start flooding the engine with fuel it doesn't want. If it fails at high voltage the opposite will happen.

 

The log I have is for the 1st drive of the day where everything ran reasonably well enough. I wasn't running the logger for the 2nd run out as it was just going to be a quick run to the store. Lemme get the laptop out and pull the log. I'll post it as csv and the adl file again. Maybe the first run before the failure will show irregularities. The 02 sensor I don't know... It has a purple wire. Not much help as the one I originally changed to some years back was changed again by the shop the last time it was in years back. I could pull it off once it cools down and see if I can get a brand on it.

 

Here's a link to both files, zipped. https://filebin.net/k6fa3enampjlvezd....7z?t=8mnkpawi

 

For what it's worth, I believe the O2 sensor is an ac delco afs20 after checking things out.

 

Can't open the files... Can you post the zip file here?

 

I think I can post the csv file, but the adl won't upload here. Lemme get the csv first.

 

and here's a link directly to the adl, not in a zip this time ...hang on, links being dumb. will edit this when its fixed

ok, fixed. https://easyupload.io/6c5xju

 

Disconnect the O2 sensor and test drive it.

GD

 

Progress. After disconnecting the sensor, the car starts and runs. Same as before the sensor failed, but it runs. Got it up to temp, but was far too worried about it dying to drive it. but it revs, sounds, well, it sounds its current normal which is fine for now. I pulled the sensor out and it looks like crap. Here's a couple pics of the offending thing. Got a new one on order for tomorrow.

 

Make sure the grounds on the back of the cylinder heads are clean and tight. One of them is a ground specific to the O2 circuit. Sounds like closed loop is trimming the fuel due to an O2 signal that's stuck rich or lean.

GD

 

I will check those. The sensor may have failed due to the failed FPR which was dumping fuel into the plenum. Unfortunately, it had likely been failing for a very long time before I worked out the issue with the FPR. All that fuel may have just destroyed the o2 sensor.

The ground straps on the back are the ones that also bolt onto the firewall, right?

 

BLMs were up to 160 toward the end of the run, indicating the ECM was reaching to a perceived lean condition.

O2 didn't appear stuck at a low voltage. But it could be sending a false signal. So yeah make sure your O2 sensor wiring and connections are good.

 

Thank you for going over this second log. I promise the next one, once I'm back up and running, will be on the new tunerpro with the definition file you wanted. Honestly, that cable I got from Moates ages ago really is a lifesaver in terms of seeing what's going on with the car.